Door locks take on various forms. In general, a door lock includes a first housing mounted to an inner surface of or disposed within the door and including a sliding bolt. The lock further includes a second housing, commonly known as a striker, attached to or disposed within an adjacent doorjamb which includes a slot for receiving the bolt when extended from the first housing with the door in the closed position. The bolt may be moved to the retracted position allowing for the opening of the door either by means of a key inserted in the lock from outside or by means of a rotatable knob located on the inside of the lock.
Security is, of course, highly desirable in lock design. The ability to break or bypass the lock permitting opening of the door from the outside renders the lock essentially useless. Many bolt-type locks have a bolt with a curvilinear, or convex, surface facing outwardly from the room into which the door is pivotally displaced when opened. The convex outer, or leading, surface of the bolt allows the bolt to engage and ride over the striker mounted to the doorjamb, followed by extension of the bolt from the lock housing for positioning within an inner recess or slot of the striker for locking the door after it is closed. While the convex, leading surface of the bolt allows for automatic locking of the door upon closure, it renders the lock susceptible to opening from outside. For example, a thin, flat object such as a plastic credit card or the blade of a metal screwdriver inserted in a gap between the door and doorjamb so as to engage the convex bolt surface may be used to urge the bolt to the retracted position, allowing the door to be opened. This is a common method for gaining unauthorized and frequently illegal entry into a secure space. This method of entry may be accomplished repeatedly without the owner or occupier of the premises even being aware of it. This unauthorized method of entry is quick, does not require the use of expensive tools or special training, and is relatively quiet.
The present invention addresses the aforementioned limitations of the prior art by providing a lock having a latch bolt with a convex outer, or leading, surface which cannot be released by the insertion of a thin, flat, object between the door and adjacent doorjamb and thus prevents unauthorized entry.